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NAD C 298 Power Amplifier With Purifi Eigentakt Amplification
nothingman
Senior Member
I have the review and measurements in front of me (would love to share but I assume it’s not kosher to post before it hits Stereophile’s website), and I don’t see where you’re getting that from. The only place I see 98db mentioned is in the mfg spec for SNR at 1W and A-weighted (JA’s SNR measurement is 95db audioband and 99db A-weighted). If you’re pulling that 98db SINAD from somewhere among JA’s THD+N measurements, I don’t see that either. I’m not the most adept at reading measurements so please don’t misunderstand this as an accusation. Would just like to clarify. I guess pretty soon everyone will see all of the measurements so it won’t be a mystery for long.
My layman’s take is it looks pretty impeccable. Not AHB2 level, but remarkably clean and load invariant for the power, features, and price.
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OP
- Thread Starter
- #643
Check the power x THD+N graph for 4 ohms, and read the 5W point, it is about 0.0012%, which translates to SINAD 98.
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nothingman
Senior Member
Teach a man to fish! I really should have been able to figure that one out. I got fixated on the wrong graph and just wasn’t seeing it. Thanks!
got my C298 yesterday.
The Power Light flashes double and the Bridge mode indicator light once.
Version 2.1 ?
aslan7
Active Member
- Joined
- Mar 4, 2021
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The SpeakOn/Canare/ locking banana cables came. The SpeakOns make a very solid connection and are extremely convenient. Forgot to mention that the VTV case is really solid and well made. The C298 looks great and has many features but I like the simplicity of the Eval 1. My only experience with Class D was with a Wyred 4 Sound integrated which was very satisfactory but I didn’t need any of the numerous preamp features and it is big. I guess I’m done with equipment and can sit back and enjoy the music.
I've been having some issues using the auto-sense function with a low variable gain setting (8.5dB), using a miniDSP SHD as the source, and I wondered if anyone else with the same pairing could test it and see if they can replicate it (or help me figure out what's going on). When the C298 is switched on from cold and leaves standby upon detecting an input signal from the SHD (I'm using XLR connections) it outputs at a very high volume level for a couple of seconds before returning to the normal level I'd set using the digital volume control on the SHD. I assumed it was a fault with the unit or design flaw in the C298 - where it was just bypassing the variable gain setting temporarily and using the the 28.6dB of fixed gain until something switches over internally - but having returned the first unit to a NAD service centre they're insisting that there's no problem with that unit, and the replacement unit I received is exhibiting the same behaviour. This doesn't happen if the unit is manually returned to standby and leaves it again by detecting a signal, only when it's first switched on from cold. I don't have any other XLR sources or amplifiers with XLR inputs to test with, unfortunately.
For what it's worth, both of the units I've received have also had mechanical noise from the power supply in the C298, the first a fairly obnoxious hiss, the second a possibly more tolerable buzzing. I have a relatively small living room, which perhaps makes this a bit more noticeable from my listening position (about 2.5m from the amplifier) than it would be for others. The first one went to a NAD service centre where they apparently added additional materials around the inductors to dampen the noise, but it made no difference that I could discern, and they also stated that noise from this kind of power supply design is "normal". I might try moving it to a lower position in the room, the dealer seems very reluctant to accept a return.
For what it's worth, both of the units I've received have also had mechanical noise from the power supply in the C298, the first a fairly obnoxious hiss, the second a possibly more tolerable buzzing. I have a relatively small living room, which perhaps makes this a bit more noticeable from my listening position (about 2.5m from the amplifier) than it would be for others. The first one went to a NAD service centre where they apparently added additional materials around the inductors to dampen the noise, but it made no difference that I could discern, and they also stated that noise from this kind of power supply design is "normal". I might try moving it to a lower position in the room, the dealer seems very reluctant to accept a return.
My replacement unit also does as they describe, following your instructions.
Mechanical buzz and hum can be caused by DC offset in the AC power. It may be worth trying a DC blocking filter. I and another member had success with the iFi DC Blocker.
https://www.audiosciencereview.com/forum/index.php?threads/my-toroids-buzz.22587/
Thanks, I forgot to mention that I ordered one of these (the design using 6 diodes), but I returned the original unit before I could try it with that, and it makes no difference with the replacement.
What have I done wrong ?
I've tried the following at operating mode:
short press ( < 1 second ) front panel Standby button: amplifier changes to Standby mode.
press and hold front panel Standby button and then release within 1-4 seconds: no change, no blinking.
press and hold front panel Standby button and then release within 5-10 seconds: The Power Light flashes twice and the Bridge mode indicator light once, Version 2.1 ?
press and hold front panel Standby button and then release within 10-15 seconds: toggle Auto Standby mode
nothingman
Senior Member
I mean, v2.1 seems plausible to me. Would only take a quick message to NAD for you to find out. See if you can get them to tell you what changed.
OP
- Thread Starter
- #654
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So, @Kal Rubinson , in an attempt to avoid buyer's remorse from returning a C298 and purchasing an AHB2, how do you rank the two (aside from the obvious that the former is more powerful, which isn't that important to me in my desktop/nearfield arrangement)?
Rank? I hate that idea but I do prefer the AHB2 for its subjectively more transparent and revealing upper range with my Revels. With another speaker (review not yet published), that advantage was less apparent and the power difference seemed more relevant. I have bought both.
Appreciate the quick and candid response, Kal. I'm LOVING the AHB2s with my LS50 Metas, so I'm a happy camper. Thanks!
I have also made this experience with two different models (and reported it here). I have recorded the humming noise (see post 537). NAD support told me: "Since the C 298 is a completely different type of power amplifier technology than the C 268, a certain amount of noise cannot be avoided." Some members here said that I should not put up with this, so I made a third attempt and once again sent the audio recording to NAD. The answer from a higher person at NAD was: "Basically, the M 33 and C 298 are similar because they use the same power amplifier modules. Only the power supplies differ "a little" in the direct comparison of the power amp sections. And (a few weeks) later: "Unfortunately, we cannot reproduce your error here and are therefore dependent on the help of the Canadian manufacturer. We are currently still waiting for a response to our request, to which we have attached your sound recording."
End of story: the dealer has taken the device back and I remain happy with my old C 268, which is dead silent - as all my other devices.
nothingman
Senior Member
Wondered if I could ask for a bit of AHB2 vs. C298 and measurement education here.
Obviously in the Stereophile measurements the AHB2 stomps the C298 pretty handily in all things noise and distortion related. There’s just no touching the Benchmark, but for $2000 and twice the power, I think the C298 makes a good case for itself.
On the frequency response (images attached) the C298 is much better, no? It holds pancake flat regardless of load all the way out to 20k before dropping like a rock. The AHB2 starts showing significant (relative, at least) dipping starting at around 6khz into 4 and 2ohms (I think JA has a typo here actually — he doesn’t mention ”green” but mentions “red” twice, so I assume green is 2ohms). I know a lot of traditional loudspeakers don’t have much impedance around those frequencies, but some do, and take a look at something like a MartinLogan ESL impedance graph and it’s easy to see the AHB2’s response not being neutral.
Like I said, asking for a bit of an education here, and realize we’re probably splitting hairs between two very good amps. Wondered if I was right to mark that measurment in the C298’s column (all by its lonesome). Thanks.
Obviously in the Stereophile measurements the AHB2 stomps the C298 pretty handily in all things noise and distortion related. There’s just no touching the Benchmark, but for $2000 and twice the power, I think the C298 makes a good case for itself.
On the frequency response (images attached) the C298 is much better, no? It holds pancake flat regardless of load all the way out to 20k before dropping like a rock. The AHB2 starts showing significant (relative, at least) dipping starting at around 6khz into 4 and 2ohms (I think JA has a typo here actually — he doesn’t mention ”green” but mentions “red” twice, so I assume green is 2ohms). I know a lot of traditional loudspeakers don’t have much impedance around those frequencies, but some do, and take a look at something like a MartinLogan ESL impedance graph and it’s easy to see the AHB2’s response not being neutral.
Like I said, asking for a bit of an education here, and realize we’re probably splitting hairs between two very good amps. Wondered if I was right to mark that measurment in the C298’s column (all by its lonesome). Thanks.
Attachments
On paper, sure, you can score that in favor of the C298. However, as in the situations of devices competing on the basis of SINAD where the competitors all have below audible levels, I note that the worst case for the AHB2 is less than 1dB down at 20kHz. Is it significant in practice?
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